Project Summary Our goal is to develop a novel immunotherapy for the treatment of melanoma, and potentially a wide array of tumors. Although surveillance by the immune system eliminates cancer cells in some instances, tumor cells have developed a variety of mechanisms to escape immune recognition often resulting in tumor outgrowth. Immune checkpoint inhibitors (e.g. ipilimumab, nivolumab, and pembrolizumab) and cellular immunotherapies (e.g. adoptive cell transfer and CAR (chimeric antigen receptor) T cells) are showing dramatic efficacy in on- going clinical trials. However, even the most promising therapies are effective for a limited range of cancers and only for a minority of patients (e.g. response rates with PD-1 inhibitors are ~25-40%). Moreover, they can be associated with significant toxicities, and tumors ? especially solid tumors ? eventually develop resistance. The potential of B cells as anti-tumor immunotherapeutics has, to a large extent, remained untapped. Nevertheless, B cells constitute part of the cancer-infiltrating immune cells and they have anti-tumor properties including production of tumor-suppressive cytokines and enhancing tumor-killing T cell response. Indeed, the presence of B cells in the tumor microenvironment is correlated with long-term survival for cancer patients. This application is focused on advancing our preclinical development in preparation for a subsequent Investigational New Drug (IND) application to the FDA. We will determine the optimal efficacious dose of GIFT4 in murine models of cancer; assemble a toxicology package in appropriate models and optimize exprssion and develop fermentation and large-scale purification protocols. Successful commercialization would ultimately provide profound anti-tumor immunotherapeutic benefits in a wide variety of cancer indications, particularly those characterized by a weakened immune system that do not respond to other immunotherapies.